1. Field of the Invention
The present invention relates to a micro electro mechanical systems (MEMS) microphone package, and more particularly, to a MEMS microphone package that can ground-connect a metal case to a main board using an assembly process including bending and clamping an end of the case and providing a sound hole to a printed circuit board (PCB) to vary a mounting method.
2. Description of the Related Art
Generally, a condenser microphone includes a diaphragm and a back plate. The diaphragm has a flexible membrane attached to a side electrode and is vibrated by an acoustic pressure. The back plate is spaced apart from the diaphragm through a spacer and the two face each other. The diaphragm and the back plate form the parallel electrode plates of a condenser and provide electric charges between the two electrode plates by applying a DC voltage to the two electrode plates or forming an electret at one of the two electrode plates. Such a general condenser microphone is assembled in a curling manner where a diaphragm, a spacer, a base 1, a back plate, a base 2, and a PCB to which an electric circuit is mounted are sequentially stacked on a cylindrical case and then an end of the case is bent and clamped toward the PCB.
In a completed condenser microphone assembly, a distance between the diaphragm and the back plate is changed by an external acoustic pressure, which then changes the capacitance of the condenser. This change of the capacitance is processed by an electric circuit so that electrical signals are provided according to the change of the acoustic pressure.
A condenser microphone used in communication products includes an electret that is formed on a back plate with a high molecular membrane. Such condenser microphones are economical, but there is a limit to miniaturization. Thus, for extreme miniaturization of a microphone, an electrical capacity structure is realized on a silicon wafer in a die shape using a semiconductor-manufacturing technology and a micromachining technology. This electrical capacity structure is referred to as a silicon condenser microphone chip or a MEMS microphone chip. Such MEMS microphone chips must be packaged for protection against exterior interference.
A system for packaging a MEMS microphone chip is disclosed in U.S. Pat. No. 6,781,231, entitled “MICROELECTROMECHANICAL SYSTEM PACKAGE WITH ENVIRONMENTAL AND INTERFERENCE SHIELD”, issued on Aug. 24, 2004. Referring to FIG. 1, such a MEMS microphone package is achieved in a manner where a housing is formed by attaching a case 34, including a conductive layer or a conductor, to a PCB substrate 32 through a conductive adhesive 36. A MEMS microphone chip 10 and an application specific integrated circuit (ASIC) 20 are mounted to the PCB substrate 32. The ASIC 20 is configured to electrically drive the MEMS microphone chip 10 and process signals. The case 34 including a sound hole 34a is attached to the PCB substrate 32 through the adhesive 36 to protect the MEMS microphone chip 10 therein.